Thanks for your answer.
I can't get it to work. Here's a list of what I've done:
– I've made a form that makes the users able to make a post and put this on a page
– I've made a page with contains [wpuf_edit] – and I've chosen the form on the right
– I've chosen the page that contains [wpuf_edit] under settings and checked the fields “users can delete/edit their posts”
– I've made several posts and checked them in backend – the form is chosen on the right
– I still get the message: “I don't know how to edit this post, I don't have the form ID”
As I see it, I've done everything right, but maybe you can help me out.